The invention relates to a device for determining the length or the angle of rotation and comprising a diaphragm connected with a machine part and arranged between two stationary bodies of which one has a coil on a surface thereof facing the diagram. A device this type, in which a coil is arranged on a stationary body and a diaphragm is moved between the latter and a second body, is already known. A layer of electrically conductive material is arranged on the side of the diaphragm facing the coil and on a semicircular region of the front side of the second body, which likewise faces the coil. When high-frequency alternating current flows through the coil, eddy currents are formed on the, layers. Due to the screening effect of the diaphragm, the magnitude of the measured-signal voltage is determined by the diaphragm position and the position of a machine part which is connected with the diaphragm is accordingly indicated. In so doing, axial displacements, e.g. due to bearing play or to wobbling movement of the diaphragm, can influence the magnitude of the eddy current formation and can accordingly influence the measured-signal voltage. This can result in a deviation from the characteristic line of the measurement voltage curve and can result in measurement errors.